Density functional theory study of Pt₃M alloy surface segregation with adsorbed O/OH and Pt₃Os as catalysts for oxygen reduction reaction

Using quantum mechanics calculations, we have studied the segregation energy with adsorbed O and OH for 28 Pt₃M alloys, where M is a transition metal. The calculations found surface segregation to become energetically unfavorable for Pt₃Co and Pt₃Ni, as well as for the most other Pt binary alloys, in the presence of adsorbed O and OH. However, Pt₃Os and Pt₃Ir remain surface segregated and show the best energy preference among the alloys studied for both adsorbed species on the surface. Binding energies of various oxygen reduction reaction (ORR) intermediates on the Pt(111) and Pt₃Os(111) surfaces were calculated and analyzed. Energy barriers for different ORR steps were computed for Pt and Pt₃Os catalysts, and the rate-determining steps (RDS) were identified. It turns out that the RDS barrier for the Pt₃Os alloy catalyst is lower than the corresponding barrier for pure Pt. This result allows us to predict a better ORR performance of Pt₃Os compared to that of pure Pt. (Chemical Equation Presented).